Compression: the process of transforming a medium with low pressure into one with higher pressure than the inlet.

Compression ratio: the ratio of the absolute discharge pressure to the absolute suction pressure in a compressor. For example, when the absolute suction pressure is 0.1 MPa at sea level and the discharge pressure is 0.8 MPa, the compression ratio R can be calculated as follows: R = P2/P1 = 0.8/0.1 = 8.

The magnitude of the compression ratio directly affects the performance and efficiency of a screw-type air compressor. Generally, a higher compression ratio leads to higher final discharge pressure, but it also results in increased power consumption and energy losses. Therefore, when designing and using an air compressor, it is essential to strike a balance between the compression ratio and energy efficiency based on actual requirements.